High aspect ratio aircraft including light motorglider aircraft, long-endurance unpiloted air vehicles (UAVs), and long-endurance optionally piloted vehicles (OPV's) have become increasingly popular for sport and utility applications. These aircraft share a characteristic long, narrow, wing capable of generating significant lift at low airspeeds. Being aerodynamically efficient, these vehicles are well suited for long duration flight, either by soaring engine off, or by operation of fuel efficient engines. These are referred to herein as high aspect ratio aircraft.
PRIOR ART FIG. 1 is provided not for limitation, but to illustrate key features common to most high aspect ratio aircraft 100, such as most motorgliders. The wings 102 of motorgliders are typically equipped with ailerons 104, used for roll control and steering. Inboard of ailerons 104 are flaps 106, typically provided to increase lift at low airspeeds and typically configured such that the flaps 106 of both wings operate simultaneously so as to not interfere with roll control or steering. In some motorgliders, the functions of flaps and ailerons are combined into a flaperon surface on each wing, where common deflection performs the function of flaps, and opposing deflection performs the function of ailerons.
Since motorgliders 100 typically have very low drag, with glide ratios of as much as sixty to one; retractable spoilers 108 or air-brakes are provided that, when deployed, increase drag and reduce lift, thereby steepening glide to facilitate landing. Typically, the spoilers of both wings are coupled together such that they deploy simultaneously and do not interfere with roll control or steering.
A horizontal stabilizer 110 is also typically provided, with an elevator 112 configured to provide pitch control, and a vertical stabilizer 114 equipped with a movable rudder 116 for yaw control and steering.
Typical motorgliders are also equipped with a propeller 118 that is coupled to an engine and configured so that propeller drag may be reduced when the engine is not operating; various models are configured for drag reduction by retraction of the propeller into a nosecone, retraction of propeller along with a pylon-mounted engine, or by feathering the propeller. The engine is typically configured such that it is usable to launch and fly the motorglider to areas of rising air may be found, such as may result from thermal activity or from the interaction of wind with steep terrain. The engine is also typically configured to be shut down during flight, and restarted during flight.
For landing and takeoff, landing gear with one or more wheels 120 are typically provided, in many motorgliders one or more of wheels 120 are retractable to reduce drag. In some embodiments, these are in tricycle configuration with a forward nosewheel and two main-gear wheels located aft of a center of gravity, in other embodiments they are in conventional configuration with two main-gear wheels located forward of center of gravity and a tailwheel, and in yet other embodiments they are arranged with a central main wheel and smaller wingtip and tail wheels as are often used on gliders. Since common causes of damage to retractable-gear aircraft include wheels-up landings and premature retraction at takeoff, wheels 120, if retractable, are typically equipped with a “weight on wheels” or “squat switch” sensor to detect ground contact, typically sensing weight on wheels 120 and prevent retraction while on the ground; and with both gear-down sensors and gear-up sensors that are coupled to indicators in cockpit 122. In some embodiments, separate gear-down sensors and gear-up sensors are provided for each wheel 120.
Since wings 102 of motorglider and other high aspect ratio aircraft are long relative to typical powered aircraft of similar weight and height, some flight maneuvers commonly performed in typical powered aircraft are difficult, if not impossible, to perform in motorgliders. For example, a typical powered aircraft may perform a “slip” while making a crosswind landing on a runway, lowering the upwind wing and permitting the aircraft to keep its longitudinal axis 124 better aligned with the runway than otherwise possible. With a long-winged motorglider, a “slip” during landing may cause the wingtip to impact the ground before wheels 120 reach the runway. Similarly, use of ailerons 104 on long wings to turn the aircraft cause more adverse yawing movements than those encountered with typical powered aircraft. Further, the low stall speed helpful in riding thermals makes motorgliders far more vulnerable than conventional light aircraft to unintended liftoff or loss of control in gusty conditions during takeoff, landing and ground operations.
Typical light aircraft use flaps to increase drag and lift for takeoff and landing, while at all other times the flaps remain fully retracted. The pilots of motorgliders, however, use different flap settings from reflex (negative or upward) deflection for high speed flight between thermals to positive (downward) deflection settings to optimize the wing profile for slower speeds while in thermalling flight. Timely and accurate application of flaps 106 adapts the wing and significantly improves a motorglider's performance. Given the limited number of discrete flap positions, the pilot of a traditional motorglider must accept an approximate setting and can never set the perfect flap setting which may lie between one of the preset flap settings.